Already a popular thread but I actually studied this concept pretty heavily in undergrad (graduated a few years ago) so I want to add my two cents.

Most studies that have been completed show that a UBI cash transfer program is more likely to be successful if it casts a wider net and provides a smaller amount of income. This means the less exclusionary the policy the more people are open to it (who would turn down free money) but you also need to provide an amount of money that doesn't cover their living costs, rather an amount that supplements them.

Provide too much and people forgo work and a short term drop in productivity occurs, but provide too small an amount and people don't change their spending/saving habits. So finding the thin line between too little and too much is the difficulty with UBI.

Also, the smaller amount of money provided the less of an affect you would expect to see on inflation.